1. Field of the Invention
The present invention relates to a system and method for selecting reliable communication links between nodes in a wireless ad-hoc communication network. More particularly, the present invention relates to a system and method for using bit error rates of transmissions between a mobile or stationary node and its neighboring mobile and stationary nodes in a wireless ad-hoc communication network, to determine with which of those neighboring nodes reliable uni-directional or bi-directional communication links exist.
2. Description of the Related Art
In recent years, a type of mobile communications network known as an “ad-hoc” network has been developed to address the needs of multiple mobile device communication beyond traditional infrastructure coverage. In this type of network, each user terminal (hereinafter “mobile node”) is capable of operating as a base station or router for other mobile nodes within the network, thus eliminating the need for a fixed infrastructure of base stations. Accordingly, data packets being sent from a source mobile node to a destination mobile node are typically routed through a number of intermediate mobile nodes before reaching the destination node.
More sophisticated ad-hoc networks are also being developed which, in addition to enabling mobile nodes to communicate with each other as in conventional ad-hoc networks, further enable the mobile nodes to access fixed networks and communicate with other types of user terminals, such as those on the public switched telephone network (PSTN) and the Internet. Details of these advanced types of ad-hoc networks are described in U.S. patent application Ser. No. 09/897,790 entitled “Ad Hoc Peer-to-Peer Mobile Radio Access System Interfaced to the PSTN and Cellular Networks”, filed on Jun. 29, 2001, in U.S. patent application Ser. No. 09/815,157 entitled “Time Division Protocol for an Ad-Hoc, Peer-to-Peer Radio Network Having Coordinating Channel Access to Shared Parallel Data Channels with Separate Reservation Channel”, filed on Mar. 22, 2001, and in U.S. patent application Ser. No. 09/815,164 entitled “Prioritized-Routing for an Ad-Hoc, Peer-to-Peer, Mobile Radio Access System”, filed on Mar. 22, 2001, the entire content of each being incorporated herein by reference.
In such ad-hoc networks, data flow is from node to node, and relies heavily on optimum route selection. Factors such as transmission power consumption and pipeline delays play a critical role in selecting transmission routes through the network which satisfy minimum requirements. For example, certain service classes such as the transmission of voice data, requires a minimal pipeline delay. However, minimizing pipeline delays often increase transmission power levels, which may overly burden the limited power supply of mobile nodes. Furthermore, the transmission itself requires the establishment and use of reliable communication links between nodes.
The challenge in identifying reliable links in an ad-hoc network lies in the fact that many communication links may be intermittent, unidirectional, or constantly varying in an environment where communication between nodes is sometimes difficult, even during normal operation. One indication of poor communication links between nodes is the detection of a bit error rate (BER) which exceeds allowable limits. The detection and use of bit error rates in wireless communication is discussed in U.S. Pat. No. 5,771,467 to Yukio Sato, which is incorporated herein by reference. As described in the Sato patent, the BER is constantly monitored and compared to a threshold value. The detection of a BER exceeding the threshold value halts communications between devices until the BER falls below the threshold. The Sato patent discloses a mobile station which prevents data communications when circuit quality has degraded below a threshold value, as indicated by a large BER. However, Sato does not address the location of nodes with which communication exceeds minimum BER levels, such nodes being critical to establishing a set of reliable communication links. Accordingly, a need exists for a system and method to determine bit error rates present during communication with area nodes, and creating a list of nodes having reliable links based upon the BER.